With the recent growth in numbers of communication satellites in orbiting operation around the earth, the number of receiving stations has grown explosively in the last few years. Each of these receiving stations requires an antenna capable detecting signals at levels in the range of -120 dbm to -30 dbm while rejecting terrestial interference (TI) and capable of polarization control employing a servo motor. It is further desirable for maximum utility that a single feed assembly exhibit the capability of operating simultaneously in two different frequency bands, for example, the C band of 3.7 to 4.2 GHZ and the Ku band of 11.7 to 12.2 GHZ or the optional Ku band of 10.95 to 11.7 GHZ.
It is desirable for dual frequency feed assemblies to have their probe axes coaxial with a common reflector for maximum received signal strength at each frequency and to minimize unwanted side lobes. Coaxial mounting of dual frequency feeds without cross coupling and interference has not been effectively achieved heretofore. Studies have been made of input mismatches developed in TE11 mode coaxial feeds as well as the use of irises and their effects in coaxial waveguides. These studies, while helpful, have not given clear guidance for the design of an optimum dual frequency band coaxial feed assembly.
One attempt at a coaxial C and Ku band receiver antenna employs a pluraity of wires surrounding the Ku band aperture to bypass it as an obstruction and introduce it into the C band polarizer behind the Ku band assembly. A common servo motor rotates the Ku band and C band probes.